Mercury levels found in remote Pacific trenches are unprecedented •

An international team of researchers has discovered amounts of highly toxic mercury in the deepest trenches of the Pacific Ocean that exceed any value ever recorded in distant marine sediments.

Experts report that the mercury levels that have accumulated in the remote Pacific are even higher than in many areas directly contaminated by industrial discharges.

Researchers have obtained the first-ever direct measurements of mercury deposition in one of the most difficult environments to sample on Earth.

Principal author of the study, Professor Hamed Sanei is the director of the Lithospheric Organic Carbon (LOC) Laboratory at the Department of Geosciences at Aarhus University .

“The bad news is that these high levels of mercury may be representative of the collective increase in anthropogenic Hg emissions in our oceans,” said Professor Sanei. “But the good news is that ocean trenches act as a permanent dumping ground, so we can expect the mercury in them to be buried for millions of years. Plate tectonics will transport these sediments deep into the earth’s upper mantle.

“But even if the mercury is removed from the biosphere, the amount of mercury that has ended up in ocean trenches is still quite alarming. It can be an indicator of the overall health of our oceans. “

Co-author of the study, Dr. Peter Outridge is a research scientist at Natural Resources Canada and lead author of the United Nations Global Mercury Assessment.

“The results of this research help fill a key knowledge gap in the mercury cycle, namely the actual rate of removal of mercury from the global environment in deep sea sediments,” said Dr Outridge. “We have shown that sediments in ocean trenches are ‘hot spots’ of mercury accumulation, with mercury accumulation rates several times higher than previously believed.”

Study co-author Prof Ronnie Glud, director of the Hadal Center at the University of Southern Denmark, was the chief scientist of a multinational expedition to the ocean trenches.

“This paper calls for additional extensive sampling of ocean depths and in particular of the hadal trenches to support this preliminary work,” said Professor Glud.

“Ultimately, this will improve the accuracy of environmental mercury models and the management of global mercury pollution.”

The study is published in the journal Scientific reports.

Through Chrissy sexton, Editor

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